U.S. investigators believe they have identified a Kuwaiti lieutenant of Osama bin Laden as the likely mastermind of the Sept. 11 terrorist attacks, a senior U.S. counterterrorism official said Tuesday.

Khalid Shaikh Mohammed, designated one of the FBI's most-wanted terrorists, is at large in Afghanistan or nearby, the official told The Associated Press.

U.S. investigators believe Mohammed planned many aspects of the Sept. 11 attacks. "There's lots of links that tie him to 9-11," the official said, speaking on condition of anonymity. "He's the most significant operational player out there right now."

Within three months of Sept. 11, according to the official, the FBI learned that Mohammed had transferred money that was used to pay for the attacks and since then the United States has gathered other substantial evidence pointing to him as the key planner.

Mohammed is accused of working with Ramzi Yousef in the first bombing of the World Trade Center, which left six dead in 1993. He and Yousef, hiding in the Philippines, also are accused of plotting in 1995 to hijack and bomb several trans-Pacific airliners heading for the United States. (Albawaba.com)